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TY P E K C-4 R ELAY
BUS L
�
TRIP
ey_s � BKR 4
868
� =�gc�
SING
L � BKR I
868
� ����
SING
L
�
BKR 4
868FI
ICE
TRB-2
KC-4
62
TD-:5
62X
AU
878
04T
8KR.2 FAILURE DETECTION
� '50-2.
10
868F2
DESCRIPTION
NO.
REO'D OWG.
NO
ZENER TRIPPING UNIT
3/BAY+I 187A696
OVE"RCURRENT DETECTOR
1 /BKR.
188A640
POWER CIRCUI T BREAKER
3/BAY
BREAKER FAILURE TIMER W/TX
1/BKR.
3515AI7
B.F. INITIA.TE AUX.-PRI
II LINE
3500A85
B F. INITIATE AUX.-BACKUP
1 /LINE
3500A85
B.F. INjTIATE AUX.-BUS
II BUS
3500A85
US DIFF. LOCKOUT AUX.
I/ BUS
B F. LOCKOUT AUX.
1/BII:R
BUS OIFF. RELAY
1/BUS
TRIPPING AUX.
J/LINE
3S00A88
4
"HIGH-THRESHOLD TYPE(4MS PICKUP)
••
=WITH SUPERVISING LIGHT, USE EITHER 868 CONTACT OR TRB-2
t ..
������
NA
<t
zf�Nl�E
���
�
�
O
J
F
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HAND 62Y CONTACTS.
1428Cl8
Sub 5
Fig. 4. External Connections for the KC-4 Relay - Breaker Failure Protection of a Breaker-and-a-Half Bus Arrangement -
One Timer
per Breaker.
plished by line relays, so these actions are re
dundant. However, the blocking of reclosing for
breaker 2, and reclose blocking at the remote
terminal via the transfer-trip signal, are now
provided. Also, 86B-L now strips bus L to isolate
the failed breaker l .
Now, refer to the breaker
2
failure detection
circuit.
BFI
is
provided by 62X and Y contacts for
lines A and B, since a fault on either initiates
tripping of breaker 2 . If breaker 2 fails and the
timer 62 delay expires, lockout switch 86BF is
energized. Contacts of 86BF trip breakers l and
3 ,
block reclosing o n all
3
breakers, and transfer-trip
lines A and B. Some of these actions are redund
ant-for example, a line A fault does not require
re-tripping of breaker
1 .
But none of these re
dundant actions are detrimental. Remember that
transfer-tripping of the remote end of the faulted
line isn't really redundant since it performs the
important additional function of blocking re
closing at the remote terminal.
The TX relay is shown providing optional seal-
in of BFI contacts as described for the single-bus
single-breaker case above.
As mentioned before, on breaker failure
protection, a separate timer for each breaker has
an advantage over a common timer per bus, and
also most of the breaker-and-a-half bus arrange
ments are applied to the rather high voltage
system. Therefore, it is recommended that a
separate timer be applied for each breaker for
the breaker-and-a-half bus arrangement.
R I N G B U S ARRA N G E M E NT
Figure
5
shows the line and breaker-failure
protection circuits for a ring bus. The symmetry
of the bus permits a simple circuit for the latter
function. Using breaker 2 as an example, BFI is
provided by 62X and 62Y contacts from lines A
and B, since a fault on either line initiates breaker
2 tripping. If the time delay expires, the lockout
switch 86BF trips adjacent breakers 1 and
3 ;
blocks reclosing o f breakers
1 ,
2, and
3 ;
and
transfer-trips both line A and line B. As in the
breaker-and-a-half scheme, redundant actions are
7
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Summary of Contents for KC-4
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